It is now recognized that the pigment epithelium plays an important, and essential, role in the visual process. The purpose of the present study is (a) to examine systematically the biochemistry and enzymology of the retinal pigment epithelium, and (b) to relate this information to specific functional and morphological properties of the cells. With this as a general framework, two aspects of retinal pigment epithelial enzymology will be examined in detail using cattle eyes. These are: i. enzymes which function in the degradation of phagocytized rod outer sigment discs, and ii. the role of the pigment epithelium in the metabolism and turnover of vitamin A compounds. Included in the latter will be studies on the hydrolysis of labeled retinyl esters and in addition, detailed examination of the fate of the retinol liberated, particularly as it applies to retinol-binding protein(s) that are thought to be present in these cells.